Optical materials employing microstructures that exhibit the property of birefringence are commonly used to generate harmonic energy around light wavelengths. These materials are useful for frequency doubling, tripling or multiplying one or more fundamental inputs. Layered crystal structures are known to exhibit practical nonlinear transmission of light energy that usually result in harmonic generation with efficiencies that are generally low. Attempts have been made to optimize the harmonic generating efficiency of various materials by orienting molecules sandwiched between substrate materials. In U.S. Pat. No. 5,589,235, an applied magnetic field is used to pre-align molecules, and then a source of radiation is used to cross-link the molecules so that they maintain their position after the magnetic field is removed. In another attempt to fabricate a device that exhibits high harmonic generating efficiency, U.S. Pat. No. 5,380,410 describes a method by which periodic electrodes may be fabricated to provide inversion regions that improve the efficiency of a ferroelectric material which exhibits an intrinsic nonlinear optical property. The fabrication of a nonlinear optical region or layer on a material that generally has inherently linear characteristics is disclosed in U.S. Pat. No. 5,157,674 which teaches a process by which a charge transfer dopant is introduced to produce a semiconducting region on a bulk glass or microcrystalline substrate.
One apparent drawback to these approaches is wavelength-dependent attenuation. This attenuation occurs when lightwave energy propagates through lossy materials, resulting in attenuation. In general, both polymer and glass substrate materials exhibit high attenuation through absorption in the near UV and UV regions. Microcrystalline materials that utilize birefringence generally must have sufficient light path propagation length to produce sufficient phase changes for significant harmonic generation. Longer path lengths usually result in even greater attenuation.
Researchers have had to resort to modification of bulk materials or orientation of molecules in a solution or matrix to produce structures that exhibit optical nonlinearity, and usable harmonic generation. These researchers have not been able to successfully utilize practices that are now common in the electromagnetic radio electronics fields, even though light waves are merely electromagnetic waves of short wavelengths, primarily because techniques and materials for the fabrication of practical electromagnetically responsive elements in the small sizes necessary for efficient use at light wavelengths in the ranges of 10,000 nanometers and shorter are not available. Optical crystal materials and composite materials, due to their structure, make it difficult to optimize the orientation of individual electromagnetically responsive elements.
An important aspect of successful fabrication and use of radio frequency nonlinear harmonic generating materials is the ability to control the orientation and sizes of those elements with respect to various electromagnetic fields. This is possible since radio frequency waves, and even microwaves, are relatively long. Developers of nonlinear, harmonic-producing devices for radio wave applications have been able to successfully fabricate numerous circuits, cavities, transmission lines, junctions and other structures scaled to radio wavelengths. This practice has been extended over time to include VHF, UHF, microwave and so-called millimeter wave regimes, and has included discrete components, transmission lines and antenna systems that have been scaled down to operate optimally at ever-higher frequencies.
Designers have also been able to fabricate nonlinear junctions that are small with respect to the wavelengths involved. These junctions are capable of rectification, mixing, detection and amplification over a portion of the full cycle of the alternating current, electromagnetic wave energy, and include conventional diodes, Shottky diodes, tunnel diodes, transistors, field effect transistors, bipolar transistors including discrete components and mass array fabricated devices such as integrated circuits and linear and two-dimensional arrays.
It would be logical to extend this practice into infrared, lightwave and ultraviolet regimes if the materials, designs, and techniques needed to accomplish these developments could be understood and executed. Work toward this goal is proceeding today with limited success. It has been suggested that carbon nanotubes, also known as C.sub.60 or fullerene structures, could be used as part of such electronic devices that would operate efficiently in the optical domain. Researchers have had limited success with films of C.sub.60 that have appeared to have properties that are both electronic and optical, and initial attempts at producing components have been made using layered, deposited and more-or-less random length coatings of this and other polymeric conductive materials, but efficiencies, though improved, are still not optimized, and design criteria for practical devices are still not developed.
It would be desirable if junctions, elements and conductors could be fabricated that operate in the regime of light wavelengths in a way that made them efficient, repeatable and manufacturable. It would be desirable if these junctions, elements or conductors were configurable to provide efficient nonlinear transfer characteristics that could be used for generating harmonics, mixing, modulation, frequency multiplication, and amplification of lightwave signals in addition to more linear antenna-like properties such as resonance, charge storage and reradiation of electromagnetic field energy. Many useful applications would be found for the successful highly efficient nonlinear optical material, device or technique that could convert infrared energy to visible lightwave energy and to ultraviolet lightwave energy in an efficient manner. It would be particularly desirable if the devices could be produced quickly and inexpensively, and if their characteristics could be controlled effectively using known manufacturing process control techniques.
SUMMARY OF THE INVENTION
The invention features a light responsive electromagnetic conductor placed in electrical contact with a junction exhibiting polar, nonlinear electrical transfer characteristics. The invention allows conversion of radiant light frequency energy to a conducted electron charge transfer across a semiconducting junction, and subsequent conversion and reradiation of a portion of the energy to lightwave energy at a multiple of the light frequency. In one aspect, a method of generating harmonic energy near light wavelengths is described comprising the steps of exposing a conductor to an infrared, visible or ultraviolet electromagnetic light energy having an alternating waveform inducing a current with electromagnetic energy in the conductor to cause an electrical charge to cross a junction, and emitting at least a portion of the energy at a harmonic multiple of the light energy.
In one aspect, the invention relates to the use of a substrate material to support carbon nanotubes which are used as frequency selective electrical conductors. In one embodiment, the conductors are polarized with respect to the substrate. In another embodiment, a foraminous substrate is used to influence and support the orientation of the electrical conductors. In another embodiment, the foraminous substrate supports a nanoparticle which creates at least a portion of a nonlinear electrical junction. In another aspect, the invention relates to a conductive element with a non-linear charge transfer region that is small with respect to that element.
In one aspect, the invention relates to an antenna structure that admits and radiates at light wavelengths. In another aspect, a lightwave electromagnetic antenna having a linear conductor is attached to a substrate material, with the linear conductor having an electrical length sized to respond to an electromagnetic light wavelength. In another aspect, the invention relates to antennas with conducting elements of less than 2000 nanometers in length that operate near light wavelengths. In one embodiment, the conductors form a traveling wave structure. In another embodiment, the conductors are arranged to form a log periodic structure.
In another aspect, the invention relates to a conductive element with an electrical length about a multiple of 1/4 wavelength of a light wavelength. In one embodiment, the electrical length of the conductor inclusive of a junction may be about 600 nanometers corresponding to 1/2 wavelength of infrared light. Impinging infrared light energy is collected; rectified and reradiated at a multiple of the infrared light frequency with high efficiency. In another embodiment, the electrical lengths of the conductor may be in a range from about 20 nanometers to about 2000 nanometers corresponding to ultraviolet, visible and infrared light. In one embodiment, the lengths of the conductors may be staggered to form a broadband structure. In one embodiment, the conductors are arranged in a generally parallel relationship.
In another aspect, the invention relates to an array of conductive elements with electrical lengths around a multiple of 1/4 wavelength of light, arranged so that at least one optical port and at least one electrical port, are held in communication via a nonlinear junction. In one embodiment, the electrical port is a terminal on a optical device which modifies a charge transfer characteristic of a junction. In one embodiment, a device for rectifying an alternating waveform occurring around light wavelengths is comprised of a short conductor of less than 10,000 nanometers in length and a nonlinear region with an electrical length less than the light wavelength. In another embodiment, the nonlinear junction region consists of a nanoparticle. In another embodiment, the junction is a polarized, doped region with an electrical length shorter than 1/2 of the light wavelength.
In another aspect, the invention relates to the process by which the growth of lightwave antenna elements upon a substrate may be controlled by observation of an optical property. In one embodiment, various lengths of nanotubes are grown in a controlled manner upon the substrate.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.